Method of recovering uranium from underground deposit



METHOD OF RECOVERING W UNDERGRGUND DEPOSIT No Drawing. Application June 10, 1954' Serial No. 435,940

3 Claims. (Cl. 262-3) FROM This invention relates to the recovery of uranium, vanadium, and equivalent elements, and is particularly directed to the provision of an improved method for recovering such elements from underground deposits more efficiently and more economically than has been possible heretofore. This application is a continuation-in-part of my prior application Serial, No. 202,867, tiledtDecember 27, 1950, now abandoned.

At present many of our carnotite (uranium and vanadium) mines are rather small undertakings, in part because of the irregular distribution and, smallness of many of the orebodies on the Colorado Plateau. These ore deposits are usually in remote regions and frequently do not warrant great capital investment in equipment. Relatively primitive methods are therefore often used. In the better of the small mines, shallow inclined shafts lead to irregular regions of rooms and pillars mined by one to five men using breast stoping techniques. The poorer sites are one-man gopher-holes. The ore breaks readily with simple dynamiting. In the past much valuable material has been left behind in pillars supporting weak roofs. No efiort is made'to monitor the concentration ofdangerous gases and dusts in working areas. (Occasionally wet drilling is used tominimize dust.) Costs of mining even shallow deposits by these methods are relatively high per ton of ore handled. Only high prices and rich'ores permit profitable operation of many of the deposits.-

In the future, when mining operations will be forced to more difiicult sites and to greater depths for ore, the safety and economy problems will become even more serious. The remoteness of the mining regions will continue to make for relatively high costs and labor turnover, indicating the need for mining methods with little need for underground man power.

My invention, in simplest terms, consists of an improved process, especially suited to mining carnotite and similar ores of the Colorado Plateau, by direct leaching of the mineral values from the underground ore deposits. The method of the invention comprises delivering a cold dilute aqueous solution of an alkali metal salt of carbonic acid, substantially at ground temperature, into direct contact with the underground uranium (or vanadium, or other equivalent) mineral deposit, recovering the solution containing dissolved uranium from the deposit, and recovering uranium from the solution.

While it has long been known that the more common uranium minerals are soluble in alkali metal carbonate solutions, it has heretofore been considered necessary for the solutions to be hot and concentrated in order to dissolve the uranium efiiciently and reasonably completely. I have found, however, that eflicient recovery of uranium by direct leaching in place of underground deposits can be efiected using dilute solutions (containing less than 50 grams per liter of the active solvent) at a temperature no higher than the temperature of the ground in which the deposit occurs, particularly if the leaching Patented July 28, 1959 solution is maintained in contact with the mineral for a prolonged period of time.

It will be useful to describe first the general geologic setting for which this invention is most suited. To date most of the carnotite mine locations are at sites accidentally exposed as outcrops by deep river'valleys and canyons cutting through the pregnant stratum. The mines are either shallow entries from the surface or in the sides of the exposed valley clilfs. One may expect that orebodies more subtly hidden will in the near future yield to the more powerful exploration methods in development. Geologic sections indicate that many will be overlaid with several thousand feet of overburden, thus presenting major mining problems.

The microscopic geology is. also significant. It seems apparent that the carnotite minerals were deposited by circulating solutions in the sandstones soon after the sandstones were laid down. The carnotite crystals are situated on the outside surfaces of the sand grains and in the interstices of the generally porous structure. This circumstance has led, for instance, to some successful 'work' in differential grinding techniques for concentrating theores. The permeability of the sandstone varies rather Widely, ranging from that typical of coarse building sand to that of rather well-compacted quartzite, compacted, no doubt, after deposition. of the carnotite. The average material. is porous and is readily permeable to circulating fluids.

Uranium in its geologic occurrences is either in the plus four or plus six valence state. In the sedimentary geology with which we are wncerned at present it is almost always in the plus six state as the combined uranyl ion, UO It may be brought into aqueous solution by both acid and alkali solvents.

In order to increase the solubility of uranium in the cold leach solution which is employedin accordance with the invention, it is useful to incorporate complexing agentscapable of forming little-ionized complexes with uranitun-bearing ions. Among the complexing agents which can be used effectively for this purpose are sub stances which yield oxalate, salicylate, malate, maleate, tartrate, phosphate, acetate, lactate, pyruvate, glyceryl phosphate, proteinate, acetylacetonate, sulfate, fluoride, ammonium mercapto acetate (thioglycolate), thenoyltrifluoroacetone, and sulfo-salicylate ions. These may function by forming complex ions with uranium, from which the uranium shows little tendency to dissociate, or they may function by forming soluble salts which remain relatively unionized in solution. In either event, the complexing agents reduce the amount of solvent required to extract the uranium efiiciently from the underground mineral and to produce leach solutions containing a reasonably high concentration of uranium. In addition to the. substances mentioned above, sucrose and formaldehyde havebeen found useful as complexing agents.

When, as quite often occurs, the uranium mineral is foundin .a deposit which is associated with a carbonate or other acid-consuming gangue, the invention contemplates using an alkaline leach solution comprising an aqueous solution of an alkali metal carbonate. (However, the use of such alkaline leach solution is not confined -to ores that occur in acid-consuming gangue. These alkaline leach solutions can also be used when desired to recover uranium from ores that occur in a siliceous or other acid-insoluble matrix.) By the term carbonate I include not only the normal carbonates, but also the bicarbonates. Sodium and potassium (especially the former) carbonates and bicarbonates are the substances preferably employed in making up the alkaline leach solutions, although ammonium carbonate can be used with success, and for purposes of this specification, I include the ammonium salts in the term alkali metal carbonate.

While dissolution of uranium in carbonate leach tions appears to involve formation of a little-ionized 3 The carbonate leach solution used inaccordance with the invention contains in general less than 50 grams per liter of dissolved carbonates, and isprepared and used cold (i.e. at substantially atmospheric temperature or at therefore it is desirable for the solution to remain in contact with the underground uranium deposit. for a prolonged period of time, inorder' toassure efi'icient extraction of uranium from the deposit and the formationof reasonably concentrated leach solutions.

solucomplex'w ith the carbonate ion itself, it is possible nonetheless touse other complexing agents, as set forth above,

in lea-ch solutions employing an alkali metal carbonate as A the active solvent. Substances yielding citrate ions in the leach solution are especially advantageous complexing agents to employ when an alkali metal carbonate is the active solvent, but other complexing agentsas listed above may be employed if desired.

To facilitate dissolution of uranium from the deposit,

3 i and especially-in operating on deposits'wherein the fluid.

with the provision of any particular method for separating the uranium from the recovered leach solution. Any

' convenient or desirable method may be employed for thisconsuming gangue which comprises delivering a cold convenient arrangement. For example, an array of drill holes may be driven into the deposit from the surface of the ground, and thesolvent may be delivered through one or more of these drill holes and then pumped to the surface again through others. Other procedures heretofore proposed for conducting leach solutions to and from underground deposits in carrying out leaching-in-place operations may also be employed.

Uranium is recovered from the leach solution in any convenient manner. It may for example be precipitated as sodium diuranate (Na U O- for alkali metal carbonate solutions by the addition of caustic soda. It may be recovered as uranyl nitrate by extracting the leach solution with dimethyl ether after adding a nitrate thereto, and then distilling off the ether. Similarly, many other organic liquids are known and can be used for extracting the uranyl nitrate (and other uranium compounds) from the leach solution. If desired, the uranium may be precipitated by treatment of the leach solution with caustic soda and the precipitated sodium diuranate may be further purified by dissolving it in nitric acid and separating it from impurities by solvent extraction with ether or other organic compound. Recovery of the uranium, either directly from the leach solution, or from an organic solvent into which it has been incorporated by solvent extraction, may be ettected using an ion exchange resin.

purpose. 4

A particular feature of the method of this invention resides in the safety with which it can be employed. Itinvolves minimum exposure of operating personnel to radiation, and it avoids the need forexposure of mining personnel to hazardous dusts and gases.

I claim: 1. The method of recovering uranium from an underground deposit of a uranium mineral dispersed in an acidaqueous solution containing less than 50 grams per liter of an alkalimetal carbonateinto direct contact with the underground deposit in situ, the temperature of said solu-. tion being substantially-the sameas the temperature of the deposit, maintaining the solution. in contact Withthe uranium-bearing deposit for a prolonged period of time,

- then recovering the solution from the deposit, and recovering uranium from the solution.

2. The method according to claim 1,

solution includes an oxidizing agent.

3. The method according to claim 1, in which the solution contains a complexing. agent capable of form ing littl6-ionized complexes with uranium-bearing ions.

References Cited in the tile of this patent UNITED STATES PATENTS 565,342 Frasch Aug.4, 1896 1,001,480 Ulzer et a1. Aug. 22, 1911 1,050,796 Bleecker Jan. 21, 1913 1,649,385 'Blumenberg 's Nov. 15, 1927 1,690,446 Grant et a1. Nov. 6, 1928 1,999,807 Gibbs will"- Apr. 30, 1935 2,172,683 Reed Sept. 12, 1939 2,173,523 Nye et a1 Sept. 19, 1939 2,180,692 Potter Nov. 21, 1939 2,388,009 Pike Oct. 30, 1945 2,563,623 Scott Aug. 7, 1951 2,630,369 BurWell Mar. 3, 1953 FOREIGN PATENTS 296,813 Great Britain Sept. 10, 1928 OTHER REFERENCES Handbook of Nonferrous Metallurgy, Recovery of Metals, by Liddell, pages 621, 641, published 1945, by McGraW-Hill Book Co., Inc., N.Y.

The Canadian Mining & Metallurgical Bulletin for October, 1953, Montreal, vol. 46, issue 498, pages 634- 644.

Mining Engineers Handbook, by Peele, 3rd Ed., vol. II, pp. 31-13, see Difierential Reagents, published by John Wiley & Sons, Inc., N.Y.

is which the i 

1. THE METHOD OF RECOVERING URANIUM FROM AN UNDERGROUND DEPOSIT OF A URANIUM MINERAL DISPERSED IN AN ACIDCONSUMING GANGUE WHICH COMPRISES DELIVERING A COLD AQUEOUS SOLUTION CONTAINING LESS THAN 50 GRAMS PER LITER OF AN ALKALI METAL CARBONATE INTO DIRECT CONTACT WITH THE UNDERGROUND DEPOSIT IN SITU, THE TEMPERATURE OF SAID SOLUTION BEING SUBSTANITALLY THE SAME AS THE TEMPERATURE OF THE DEPOSIT, MAINTAINING THE SOLUTION IN CONTACT WITH THE URANIUM-BEARING DEPOSIT FOR A PROLONGED PERIOD OF TIME, THEN RECOVERING THE SOLUTION FROM THE DEPOSIT, AND RECOVERING URANIUM FROM THE SOLUTION. 